I have a new Bosch CS-130 style alternator with a couple hundred miles on it.
Since I installed it, it's been a little noisy, but I attributed that to the brushes breaking in to mate with the slip rings.
Unfortunately, it got worse recently and has turned to a squeak. Since I don't drive the car much, the new alternator is already out of warranty (1 year) even though I've hardly used it.
Upon close inspection, I found that the alternator squeaks during one specific part in its rotation. The squeak is coming from the brushes, not a bearing.
I disassembled the alternator and found that that the front slip ring has a strange color on one spot. It looks like excess epoxy was dripped onto the ring during assembly, and this caused one of the brushes to wear it unevenly.
The bad section looks like this:
The rest of the slip ring is worn evenly:
How do I repair the slip ring surface so the brush can break in properly? Can I just turn it on a lathe? What about the surface finish?